Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Discloses internal behavior beyond annotations: resolves the registry host per extension, falls back to RDAP when port-43 is unavailable, forces a live registry lookup, and defines offer as an inference, not a quote. This adds significant context to the readOnlyHint/openWorldHint annotations without contradiction.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Description is somewhat long but front-loaded with a clear first sentence. Subsequent sentences add valuable detail on usage and offer nuance, though there is minor redundancy with the title ('registry record'). Each sentence earns its place.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter tool with no output schema, the description covers return fields, use cases, special RDAP behavior, and the offer caveat. It is self-contained enough for an agent to select and invoke correctly without further context.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema covers the single parameter at 100% with format example. Description adds minimal semantics about singular domain and registry-host resolution, but does not redefine the parameter; baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Description explicitly states 'Registry record for one domain' and enumerates contents (registrar, dates, nameservers, status codes, sale status). It distinctly positions the tool for single-domain lookups and differentiates from siblings by noting it is the only call that fills the offer field.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Provides direct usage cues: 'Use when asked who owns a domain, when it expires, or where it is hosted.' It also notes exclusivity for offer. However, it does not explicitly contrast with sibling tools for multi-domain or TLD-list use cases, so it lacks a full when-not-to-use statement.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.